Method for recovery of nitramines from aluminized energetic materials

ABSTRACT

Nitramines are one of the more expensive and often the more plentiful ingredients found in energetic materials, such as solid rocket motor propellants, explosives, and pyrotechnics. By treating aluminized energetic material with an aqueous nitric acid solution containing not more than 55% by weight aqueous nitric acid at a weight ratio of aqueous nitric acid to energetic material of about 4:1 to about 6:1, most constituents of conventional aluminized energetic materials are digested into solution, with the exception of nitramines, which remain substantially insoluble in the aqueous nitric acid and can be recovered without requiring recrystallization of the nitramines. A mineral acid other than nitric acid, preferably hydrchloric acid, is added to increase the rate of aluminum digestion. Treatment of the energetic material can be performed without volatile organic solvents, thus obviating ecological, cost, and safety concerns raised by the use of volatile organic solvents.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of filing of U.S. provisionalapplication 60/188,182 filed in the U.S. Patent & Trademark Office onMar. 10, 2000. The complete disclosure of provisional application60/188,182 is incorporated herein by reference. In the event that anyportion of the provisional application is inconsistent with thisapplication, this application supercedes the provisional application.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to the recovery of nitramines fromaluminized energetic materials. This invention is particularly usefulfor recovering nitramines from aluminized energetic materials such assolid propellants, explosives, and pyrotechnics.

[0004] 2. Description of the Related Art

[0005] Energetic materials have found widespread use, perhaps no moreextensively than in military applications, where energetic materials areused to make composite propellants for ballistic missiles and explosivecompositions for munitions and ordnances. An example of a propellantcommonly found in rocket motors and missiles is Class 1.1 solidpropellants. Like most other energetic materials used in militaryapplications, Class 1.1 solid propellants are formed from a compositioncomprising a combination of one or more of the following: polymericbinders, plasticizers, ballistic additives, chemical stabilizers, curingagents and catalysts, metal powders, and inorganic and/or organicoxidizers.

[0006] Demilitarization in the United States and abroad has created aneed for an economical, reliable, non-hazardous, and environmentallyfriendly method for disposing of the stockpile of surplus tacticalmissiles and explosives existing worldwide. Additionally, a growingnumber of larger rocket motors, such as intercontinental ballisticmissiles (ICBMs), are being and will have to be demilitarized due tointernational treaties, such as the START treaties. The disposal of suchenergetic materials is the subject of various publications and U.S.patents, including U.S. Pat. No. 4,231,822 to Roth and U.S. Pat. No.4,661,179 to Hunter et al. However, these U.S. patents focus ondisposing of explosive materials by “desensitizing” or “destroying” thematerials.

[0007] The degradation of energetic materials into an unusable state isnot the most economical alternative of disposal, since many energeticmaterials are both expensive and reusable. For example, one class oforganic oxidizer that has found wide acceptance in the rocketpropulsion, explosive, and pyrotechnic arts comprises nitramines. Commonnitramines include, for example, cyclotetramethylenetetranitramine (alsoknown as HMX and 1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane),cyclotrimethylenetrinitramine (also known as RDX and1,3,5-trinitro-1,3,5-triaza-cyclohexane), TEX(4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo-[5.5.0.0^(5,9)0^(3,11)]-dodecane),HNIW (also known as CL-20)(2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0^(5,9)0^(3,11)]-dodecane),and combinations thereof. Nitramines are commonly among the mostexpensive and highly energetic ingredients of conventional energeticcompositions. Further, nitramines are sometimes present in energeticcompositions in relatively high concentrations, such as on the order ofup to about 50% by weight of solid rocket motor propellants and up toabout 98% by weight of explosives. These factors make the successful andefficient recovery of nitramines in high yields for subsequent re-usehighly desirable.

[0008] A method for the extraction and recovery of nitramine oxidizersfrom solid propellants is disclosed in U.S. Pat. No. 5,284,995 toMelvin, which discloses the use of a liquid ammonia extraction agent forextracting the nitramines HMX and RDX from rocket motor solidpropellants. The use of liquid ammonia in nitramine recovery techniquesintroduces several complexities and expenses, especially in a closedsystem, including high capital expenditures required as outlay to obtainequipment capable of operating at the high-pressures (5 to 40 Kpsi) atwhich liquid ammonia is handled. The presence of liquid ammonia alsocreates other problems, such as worker safety issues, since contactbetween the ammonia and human skin can cause severe chemical burns tothe handler. Additionally, liquid ammonia is combustible, and presents asevere inhalation hazard if not handled correctly. Another disadvantageof the U.S. Pat. No. 5,284,995 process is that subjecting energeticmaterials, such as Class 1.1 propellants containing nitramine oxidizers,to the pressurized environments described in the '995 patent increasesthe risk of accidental detonation, as well as the accompanyingcatastrophic consequences that an accidental detonation or explosionoften has on human life and property. Yet another disadvantage of theprocess of U.S. Pat. No. 5,284,995 is that nitramines are dissolved inliquid ammonia, requiring recrystallization of the nitramines. However,the recrystallized nitramines have different particle sizes than thenitramine particles found in the propellant. Also, if recrystallizationis not performed under the right conditions, the polymorph of thenitramine changes during recrystallization.

[0009] Another method for recovering ingredients from a pyrotechnicmaterial is disclosed in U.S. Pat. No. 4,098,627 to Tompa et al., inwhich the pyrotechnic containing a cured polymeric binder is decomposedunder mild conditions. The method involves heating the pyrotechnicmaterial to a temperature of from about 50° C. to about 160° C. in aliquid medium comprising an active hydrogen-containing compound capableof cleaving the chemical bonds contained in the polymer. Representativeliquid media include mineral acids such as hydrochloric acid, sulfuricacid, phosphoric acid, nitric acid and perchloric acid, as well asprimary amines, secondary amines, ammonia, and water. The process isexpedited by modifying the liquid medium via the addition of an organicsolvent. Organic solvents reportedly suitable in the process aretoluene, xylene, dioxane, and tetrahydrofuran. The organic solventfunctions either to swell the organic polymeric binder present in thepyrotechnic material or to dissolve filler material present in thepyrotechnic material. The decomposition technique is carried out at 80°to 120° C. In practice, however, these organic solvents raise a host ofecological and safety concerns, including flammability, VOC emissions,environmentally sound and cost-effective waste disposal, and handlingexpenses. Additionally, U.S. Pat. No. 4,389,265 to Tompa et al. reportsthat the use of mineral acids and water in the manner prescribed by the'627 patent produces low yields of about 36%. Indeed, example 5 of the'627 patent reports that under the basic conditions of its process RDXmay be destroyed.

[0010] Two additional approaches for reclaiming nitramines frompropellants having polymeric binders are disclosed in U.S. Pat. No.4,389,265 to Tompa et al. The first approach utilizes a solution of2-aminoethanol in a mixture of an aromatic solvent and an alcohol todissolve the propellant binder. The 2-aminoethanol breaks down ordissolves the polymeric binder. Examples of aromatic solvents suitablefor the first approach include benzene, toluene, xylene, ethylbenzene,and diethylbenzene. Examples of alcohols suitable for the first approachinclude ethanol, 1-propanol, 2-propanol, and mixtures thereof. Thesecond approach is performed with a solution of a mineral acid otherthan nitric acid, an organic solvent, and water. For the secondapproach, examples of suitable mineral acids are hydrochloric, sulfuricand phosphoric acid; examples of organic solvents are acetone,methylethylketone, tetrahydrofuran, and mixtures thereof. The mineralacid and organic solvent combine to break down or dissolve the polymericbinder. After dissolution of the pyrotechnic binder is completed in the2-aminoethanol or the mineral acid process, the nitramine and metals, ifpresent, are removed by filtration and the nitramine is extracted inacetone. Although relatively high yields are reported in U.S. Pat. No.4,389,265, the presence of aromatic and organic solvents raisesecological and safety concerns over such issues as flammability,volatile emissions, and waste disposal. Also, the nitramine is recoveredwith aluminum fuel particulates. Consequently, separation of thealuminum requires dissolving, filtering, and recrystallizing of thenitramine. As mentioned above, recrystallization can cause the polymorphand size of the nitramine particles to change.

[0011] U.S. Pat. No. 6,063,960 discloses the recovery of nitroamines andreformulation of by-products. The '960 patent generally focuses onnon-aluminized propellants, with the exception of its mention of VTG-5Aand WAY, both of which are aluminized propellants. According to the '960patent, the propellants are treated with 60-70% nitric acid in apreferred ratio of nitric acid solution to feed of 1.0:1.0 l/kg. Thisfeed ratio calculates to a weight ratio of less than 1.5:1. Althoughthese conditions are adequate to recover nitramines from non-aluminizedpropellants containing conventional binders, in the case of analuminized propellant a substantial proportion of aluminum would not bedissolved under these conditions. Accordingly, in the event that analuminized propellant were treated by the '960 process, separation ofthe aluminum would require additional steps of dissolving, filtering,and recrystallizing of the nitramine.

[0012] Thus, it would be a significant improvement in the art to developa method in which nitramines are recovered from aluminized energeticmaterials without recrystallizing the nitramines and in which there isno need for the use of either liquid ammonia under increased pressure orhazardous organic solvents that are volatile and/or flammable.

SUMMARY OF THE INVENTION

[0013] It is, therefore, an object of the present invention to fulfill along-felt need in the art by providing a nitramine-recovery processcapable of achieving the above-discussed improvements in the recovery ofnitramines from aluminized energetic materials, especially aluminizedpropellants, without relying upon either the use of liquid ammonia underincreased pressures or the application of hazardous solvents.

[0014] In accordance with the principles of this invention, the aboveand other objects are attained by a nitramine-recovery process in whicha nitramine-containing aluminized energetic material is treated withaqueous nitric acid having a nitric acid concentration of not more than55% by weight. This low concentration nitric acid, when used inappropriate ratios relative to the aluminized energetic material to betreated, has the effect of digesting by solvation and/or solvolysismost, if not all, conventional ingredients other than nitraminescommonly found in aluminized energetic materials. As referred to herein,the term solvation means the dissolving of a solid into a solventwithout chemical reaction. As also referred to herein, the termsolvolysis means the dissolving of a solid into a solvent via chemicalreaction between the solid and solvent.

[0015] At least one mineral acid other than nitric acid is added to thedigestion process in order to facilitate digestion of the aluminum. Itis also preferred to delay the addition of the mineral acid untilsufficient time has passed for the aqueous nitric acid to digest most,if not substantially all, of the binder of the energetic material. Thetime needed for digesting the binder will depend upon several factors,including the amount of binder in the energetic material, theconcentration and amount of aqueous nitric acid, and process conditions,such as temperature. Suitable mineral acids include hydrochloric acid,perchloric acid, sulfuric acid, phosphoric acid, hydrobromic acid,hydroiodic acid. Hydrochloric acid is currently preferred because of itshigh rate of aluminum digestion. Representative concentrations ofmineral acid for use in the aluminum digestion range, for example, fromabout 1 part by weight to about 5 parts by weight based on 100 parts byweight of the aqueous nitric acid. Such concentrations are usuallysufficient to digest at least 99 weight percent of the aluminum. Aqueousnitric acid is preferably not selected as the mineral acid for aluminumdigestion. Nitric acid is relatively oxidizing compared to other mineralacids, and will oxide the surface of the aluminum to form aluminumoxide, thereby slowing the rate at which the aluminum is digested.

[0016] The nitramines remain substantially insoluble (i.e., are neithersolvated nor solvolyzed) in the low concentration nitric acid andmineral acid, and can be separated from the aqueous nitric acid, mineralacid, and digested ingredients in an efficient manner and withoutincurring great expense.

[0017] The recovered nitramines according to the presently preferredembodiment are suitable for recycling into an energetic material,including a solid propellant grain, explosive material, and pyrotechnics(known in the art as PEP materials).

[0018] There are several advantages that can be derived from theinventive process. For example, nitramine yields associated withembodiments of the present invention have been found to be much higherthan most conventional processes. In particular, nitramine yields areroutinely on the order of 90% by weight or greater according toembodiments of the inventive process. Further, the process can beperformed, and preferably is performed, free of organic solvents, thusavoiding the ecological and safety concerns and waste disposal andhandling expenses of conventional processes. Furthermore, the digestedingredients separated from the nitramine can be recovered and reused asfeed stock for commercial blasting agents, thus further reducing thewaste disposal concerns and improving the efficiency of the process. Theprocess also does not require volatile digestion agents or highpressurizes that increase the risk of unintentional detonation of theenergetic material.

[0019] The recovery method of this invention is particularly useful forrecovering nitramines from aluminized energetic materials such as solidpropellants, explosives, and pyrotechnics, and is especially useful forthe recovery of nitramines from aluminized solid rocket motorpropellants. While not wishing to be bound by any theory, it is believedthat unlike many conventional methods, in which nitramines are typicallydissolved in order to separate the nitramines from aluminum and/or otheringredients, in the present invention the aluminum reacts with aqueousnitric acid to form aluminum nitrate Al(NO₃)₃·9H₂O, which is soluble inthe aqueous nitric acid and the mineral acid is easily separated fromthe substantially insoluble nitramine. Additionally, unlike otherinorganic acids that react with aluminum to rapidly generate largeamounts of hydrogen gas and high temperatures, nitric acid has beenfound to undergo a much more sedate reaction with aluminum. The reactionof nitric acid with aluminum generates hydrogen gas and heat atmanageable rates so as to permit the hydrogen gas and heat to be removedfrom the digestion vessel. By adding a mineral acid, other than nitricacid, aluminum removal is facilitated and accelerated.

[0020] Other objects, aspects, and advantages of this invention willbecome more apparent to those skilled in the are upon reading thespecification and appended claims which, when read in conjunction withthe accompanying drawing, explain the principles of this invention.

BRIEF DESCRIPTION OF THE DRAWING

[0021] The accompanying FIGURE serves to elucidate the principles ofthis invention by illustrating a flow diagram for the extraction andrecovery of nitramines from energetic materials in accordance with anembodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS AND METHODS OF THEINVENTION

[0022] Among nitramine-containing aluminized energetic materials thatcan be successfully treated to recover nitramines are solid rocket motorpropellants. Although the method of this invention is particularly wellsuited for aluminized solid rocket motor propellants, the inventivemethod can also be applied to other materials, such as minimum smokepropellants and reduced smoke propellants containing little or noaluminum. The inventive method finds applicability to a wide array ofpropellants and propellant binders. For example, the method can be usedto recover nitramines from composite propellants, modified compositepropellants, double-base propellants, crosslinked double-basepropellants, and other plasticized and non-plasticized propellants. Asmentioned above, the present invention is not restricted to recovery ofnitramines from propellants; instead, the invention finds applicabilityto other energetic materials, including other PEP (propellant,explosive, and pyrotechnic) materials, such as plastic bonded explosives(PBX), melt cast explosives, and slurried explosives. Although theinventive process can be applied to energetic materials containing bothhigh and low concentrations of nitramines, it is most economical toapply the inventive process to energetic materials containing at leastabout 10% by weight nitramine. Representative nitramines that can berecovered by the present invention include HMX, RDX, CL-20, and TEX.

[0023] Referring now more particularly to the FIGURE, there is shown anembodiment of the present invention in which nitramines are recoveredfrom a solid rocket motor assembly. In particular, a rocket motor casecontaining a propellant, such as a Class 1.1 solid propellant grain, isprovided for the recovery process. In the illustrated embodiment, thepropellant is removed from the rocket motor case by passing waterthrough a pump or series of pumps to create high pressure water, whichis jetted into the rocket motor case and directed through appropriatenozzles at the propellant to cut the propellant from the rocket motorcase. Generally, water pressures of about 10,000 psi will suffice toremove the propellant from the rocket motor case. The selection ofsuitable pumps, valves, and jets to effect removal of the propellantfrom the rocket motor case is within the purview of those skilled in theart and, for this reason, is not discussed in greater detail herein. Itis to be understood, however, that the present invention is not limitedto the removal of energetic material from its housing by the use of highpressure water or other hydraulic treatments. To the contrary, othermechanical and chemical methods can be selected and applied to removethe energetic material from its housing or case.

[0024] In the illustrated embodiment, the propellant and water arecollected and passed to a filter, where a portion of the water used toremove the propellant from the rocket motor case is recycled back to thepump.

[0025] The propellant and the remaining amount of water (not recycled tothe hydraulic removal stage), if any, then enter into a digestion stage,where the propellant is treated with aqueous nitric acid. The propellantentering into the digestion stage preferably is present in relativelysmall pieces. For example, it is preferred that the largest dimension ofthe propellant pieces be no larger than about 2.54 cm (1 inch), morepreferably no larger than 1.27 cm (0.5 inch). Generally, it is mostefficient to extract the propellant from the rocket motor case in such amanner that the extracted propellant has the desired dimensions.Alternatively, the propellant can be subjected to a milling or grindingstep or the like (not shown) before the propellant enters the digestionstage.

[0026] One of the important aspects of this invention resides intreating the nitramine-containing propellant with a digestion agentcomprising a dilute aqueous nitric acid solution characterized by notmore than 55% by weight nitric acid. Because the aqueous nitric aciddigestion agent is relatively dilute, substantially all of the nitraminecharged into the digestion stage neither solvates nor solvolyzes in thedigestion stage, but is removed from the digestion stage as a solid. Asreferred to herein, substantially all means that at least 95% by weightof the nitramine is not digested in the digestion stage, althoughpreferably at least 98% by weight, and more preferably at least 99% byweight of the nitramine in the energetic material is not digested in thedigestion stage. The amount of nitramine that is digested (by salvationand/or solvolysis) into the aqueous nitric acid depends not only on theconcentration of the aqueous nitric acid solution, but also on the ratioof nitric acid to propellant. Generally, desirable results can beobtained by setting the weight ratio of aqueous nitric acid solution topropellant to be in a range of from about 1:1 to 6:1, although thisrange is not exhaustive as to the scope of this invention. The weightratio of aqueous nitric acid solution to propellant will generally behigher for aluminized propellants than for non-aluminized propellants.For example, the weight ratio of aqueous nitric acid solution topropellant for treating aluminized propellant is preferably in a rangeof from about 4:1 to about 6:1, still more preferably about 5.3:1.

[0027] Although the aqueous nitric acid solution used in the inventiveprocess is sufficiently dilute to avoid digestion of substantially allof the nitramine, the aqueous nitric acid solution is able to digestinto solution, by solvation and/or solvolysis, most if not all of theremaining ingredients of the energetic material. For example, nitrateester plasticizers are solvolyzed by hydrolyzing the plasticizers withnitric acid to form alcohol, which further decomposes into water andcarbon dioxide. Polymeric binders, stabilizers, and other organicingredients also are digested by hydrolysis in aqueous nitric acid.Inorganic oxidizers such as ammonium perchlorate, potassium perchlorate,ammonium nitrate, hydroxyl ammonium nitrate, and potassium nitrate, aresoluble in aqueous nitric acid, and solvated into the aqueous nitricacid.

[0028] The rate at which the aqueous nitric acid solution digests theenergetic material ingredients (other than the nitramines), as well asthe amount of nitramines (if any) that is digested into solution, dependon several factors, including the concentration of the aqueous nitricacid solution and the temperature at which digestion occurs. Theconcentration of the aqueous nitric acid solution should not be morethan 55% by weight, but preferably is at least 5% by weight, morepreferably at least 20% by weight, and still more preferably at least35% by weight concentration in order to drive the digestion reaction atan acceptably fast rate. Digestion can occur within a temperature rangeof from about room temperature (or slightly lower) to the boiling pointof the aqueous nitric acid. It is preferred to carry out the digestionwithin a temperature range of from about 30° C. to about 90° C., morepreferably about 30° C. to about 80° C.

[0029] In the illustrated embodiment, nitric acid fed via its own feedstream into the digestion stage may be concentrated or diluted. In theevent that concentrated nitric acid is fed into the digestion stage viathe nitric acid feed stream, water for diluting the nitric acid to anacceptable concentration (of not more than 55% by weight) can besupplied via the water entering with the propellant from the filterand/or via water supplied in a recycle stream from a final wash stage(discussed below). Although not shown, either of these stream and/orother water-supply stream can combine with the nitric acid prior toentering into the digestion stage.

[0030] During the digestion process, nitric oxides (NO_(X)) can begenerated, sometimes in significant quantities. The nitric oxidesgenerated during digestion can be removed from the digestion vessel byconventional means, such as, for example, a NO_(X) scrubber. Hydrogen isalso generated during the process, although at relatively slow ratescompared to processes using other mineral acids. The hydrogen gas shouldbe monitored and vented to reduce the risk of unintentional explosion.

[0031] In order to facilitate aluminum digestion, a mineral acid otherthan nitric acid may be added into the solution to digest at least aportion of the aluminum, and in a preferred embodiment at least 99weight percent of the aluminum. Suitable mineral acids include, forexample, one or more of the following: hydrochloric acid, perchloricacid, sulfuric acid, phosphoric acid, hydrobromic acid, and hydroiodicacid. Hydrochloric acid is currently the mineral acid of choice. Themineral acid may be added in a range of about 1 to about 50 parts byweight per 100 parts by weight of the aqueous nitric acid.

[0032] In accordance with the preferred version of the invention, aslurry of nitramine in the digested liquid solution and the residualaqueous nitric acid is then sent to a separator, such as a filter, wherefiltration can be performed using suitable liquid/solid separationtechniques, such as, for example, filter pressing or centrifugalseparation. The filtrate contains large amounts of nitrates, metalfuels, and oxidizers, and can be used as an ingredient for a commercialblasting agent. The nitramine is sent to a wash stage for washing withwater. The water may be filtered and sent to the digestion stage, asshown in the illustrated embodiment. Yields of nitramine of more than90% by weight, and often more than 95% by weight, can be realized.

[0033] The following examples serve to explain embodiments of thepresent invention in more detail. These examples are not to be construedas being exhaustive or exclusive as to the scope of this invention.

EXAMPLES Example 1

[0034] Into a three-necked 500 mL flask equipped with a mechanicalstirrer was added 150 mL of 55 wt % nitric acid and 10.42 grams ofsize-reduced (1.27 cm×1.27 cm×0.32 cm (or ½″×½″×⅛″)) propellant piecescontaining HMX in a concentration of 53% by weight and, as otheringredients, aluminum powder, polyglycol adipate binder, nitroglycerinplasticizer, ammonium perchlorate oxidizer, nitrate ester stabilizers,and nitrocellullose. The addition of the nitric acid created an initialexotherm, raising the temperature of the mixture to 30° C. The mixturecooled to 25° C. after several minutes, producing a propellant that wascompletely degraded into powder form after two hours of stirring. Thenitroglycerin destruction was monitored by HPLC analysis of the liquidportion of the mixture and recorded as follows (in percent destructionper hours subsequent to start of the process): 77 wt % destruction after3.7 hours; 85 wt % destruction after 5.7 hours; and 98 wt % destructionafter 22.7 hours. After 24 hours, water was added to dilute the initialacid concentration to 35 wt % and stirring continued for another 24hours. The resulting solid was collected and weighed (5.14 grams) andanalyzed by HPLC for HMX concentration (97.1 wt %) and aluminum (2.66 wt% by ICP-AES). The yield of recovered HMX (4.99 grams) was 90% by weightof the original amount of HMX in the propellant.

Example 2

[0035] Into a three-necked 500 mL flask equipped with a mechanicalstirrer was added 200 mL of 55 wt % nitric acid and 50 grams ofsize-reduced (1.27 cm×1.27 cm×0.32 cm (or ½″×½″×⅛″)) propellant piecescontaining HMX in a concentration of 53% by weight and, as otheringredients, aluminum powder, polyglycol adipate binder, nitroglycerinplasticizer, ammonium perchlorate oxidizer, nitrate ester stabilizers,and nitrocellullose. The addition of the nitric acid created an initialexotherm, raising the temperature of the mixture to 35° C., where thetemperature remained for 24 hours. The propellant that was completelydegraded into powder form after two hours of stirring. Nitrogen oxideemissions were observed after 1.6 hours. The nitroglycerin destructionwas monitored by HPLC analysis of the liquid portion of the mixture andrecorded as follows (in percent destruction per hours subsequent tostart of the process): 99.3 wt % destruction after 24 hours; and 99.6 wt% destruction after 28.5 hours. After 29 hours of reaction time, thesolid was collected (in an amount of 28.89 grams) and analyzed for HMX(90.2 wt % by HPLC), nitroglycerin (0.025 wt % by HPLC), and aluminum(8.58 wt % by ICP-AES). The yield of recovered HMX was 26.06 grams, or98% of the amount of HMX present in the original propellant. Furtheracid digestion of a two gram sample of the collected solid (in 55 wt %nitric acid at 70° C. for 6.0 hours) gave 1.59 grams of white solid. Thepurified material was analyzed for HMX (100% by HPLC analysis), lessthan 0.003 wt % nitroglycerin, and 0.009 wt % aluminum.

Example 3

[0036] Into a three-liter jacketed wide-mouth flask equipped with amechanical stirrer was added 1.8 liters of 55 wt % nitric acid. Thetemperature was adjusted to 24° C. and 450 grams of size-reduced (1.27cm×1.27 cm×0.32 cm (or ½″×½″×⅛″)) propellant pieces containing HMX in aconcentration of 53% by weight and, as other ingredients, aluminumpowder, polyglycol adipate binder, nitroglycerin plasticizer, ammoniumperchlorate oxidizer, nitrate ester stabilizers, and nitrocellullosewere added over a one-hour period, maintaining the temperature at 24° C.The temperature was maintained at 30-45° C. over the next 28 hours usingwarm water running through the jacketed flask. The propellant wascompletely degraded into powder form after two hours of stirring. Thenitroglycerin destruction was monitored by HPLC analysis of the liquidportion of the mixture and recorded as follows (in percent destructionper hours subsequent to start of the process): 75.4 wt % destructionafter 3 hours; 79.9 wt % destruction after 4 hours; and 87.3 wt %destruction after 5 hours; 94.6% destruction after 7 hours; and 100%destruction after 25 hours. After 29 hours of reaction time, theresulting solid was collected and weighed (246.9 grams) and analyzed byHPLC for HMX concentration (95.0 wt %), nitroglycerin concentration(0.011 wt %), and aluminum (3.87 wt % as measured by ICP-AES). The yieldof recovered HMX (234.6 grams) was 98% by weight of the original amountof HMX in the propellant. Further acid digestion of a 206.9 gram sampleof the collected solid (in 55 wt % nitric acid at 50° C. for 24 hours)produced 191.5 grams of pale yellow solid. The purified material wasanalyzed for HMX content (99.8 wt % by HPLC analysis), nitroglycerin(0.004 wt % by HPLC analysis), and aluminum content (0.0164 wt % byICP-AES). This represents a projected yield of 228.1 grams, or a 96 wt %recovery from the propellant of HMX. Further analysis of purifiedmaterial gave the following information: beta polymorph (FTIR), averageparticle size of 27 micron (Microtracs analysis), 0.044% acetoneinsoluble, and 0.0289% acidity.

Comparative Example A

[0037] A 125 ml Erlenmeyer flask equipped with septum, needle, stir bar,and thermometer was charged with 36 ml of 70 wt. % HNO₃. The nitric acidwas stirred and heated to 50° C. Over the next six hours a total of 5.0grams of an aluminized propellant containing about 10 to about 20 wt. %HMX was added in small portions to the heated aqueous nitric acid. Thepropellant was broken into small pieces less than 0.25 inch (0.64 cm) indiameter, prior to addition. One hour after completion of addition ofthe propellant, stirring was stopped, and the mixture filtered hotthrough a coarse frit. The filtrate was diluted with water to 200 ml andallowed to stand overnight. Precipitate was filtered off and dried togive an 81% yield.

Comparative Example B

[0038] A double base propellant comprising nitrate esters waspre-treated with hot aqueous ammonia, to destroy the nitrate esters. Theresulting powdery residue comprised approximately 25 wt. % HMX, aluminumpowder, hydrated alumina, and decomposed binder.

[0039] Following the same procedure set forth in Comparative Example A,a total of 2.00 grams of the powdery residue having an average particlesize of less than 100 microns was added, except all of the residue wasadded at once.

[0040] The mixture was then stirred and heated at 50° C. for 3 hours.The mixture was filtered hot through a coarse frit. The filtrate wasdiluted to 200 ml with water and allowed to stand overnight. Precipitatewas filtered off and dried to give a 66% yield.

Comparative Example C

[0041] A 125 ml Erlenmeyer flask equipped with septum, needle, stir bar,and thermometer was charged with 36 ml of concentrated HNO₃. The nitricacid was stirred and heated to 50° C. and 2.000 grams of a PBXexplosive, cut into 0.25 inch pieces containing 80-90 wt. % RDX, wereadded portion-wise over the next hour and a quarter to the acid bath. Nochange in temperature of the acid bath was observed upon initialaddition of the propellant. Upon completion of addition of thepropellant, the mixture was heated for an additional 15 minutes, andfiltered hot through a coarse frit. The filtrate was diluted with waterto 200 ml and allowed to stand overnight. The precipitate was filteredoff and dried to give a 68% yield.

Comparative Example D

[0042] A 125 ml Erlenmeyer flask equipped with septum, needle, stir bar,and thermometer was charged with 36 ml of concentrated HNO₃. The nitricacid was heated to 70° C. and 2.0036 grams of a solid propellantformulation comprising 80-90 wt. % RDX were added portion-wise over thenext hour to the acid bath. No change in temperature of the acid bathwas observed upon initial addition of the propellant. After all of thepropellant was added to the bath, the mixture was heated for another 1.5hours and then filtered hot through a coarse frit. The filtrate wasdiluted with water to 200 ml and allowed to stand overnight. Theprecipitate was filtered off and dried to give a 70% yield.

[0043] As demonstrated by the experiments reported above, the use of anaqueous nitric acid solution having a nitric acid concentration of 55weight percent or less resulted in nitramine recoveries of 90%, 98%, and96% for Examples 1-3, respectively. By contrast, the use of higherconcentrations of nitric acid solution produced lower yields, i.e.,81%,66%, 68%, and 70% yields for Comparative Examples A-D, respectively.

Examples 4-9

[0044] In examples 5-8, 50 grams of a propellant comprising HMX,nitroglycerin, ammonium perchlorate, and aluminum were placed in athree-neck flask with a mechanical stirrer and 400 mL of 55% nitric acidat 80° C. In Example 4, the experiment was scaled up for a 100 grampropellant sample. The propellant was added over 40 minutes. Thepropellant was heated for 4 hours at 80° C. after final addition ofpropellant. Concentrated (37 wt %) hydrochloric acid was added to theprocess for Examples 5-7. Sulfuric acid was added to the process forExample 8. The weight percents of hydrochloric acid and sulfuric acidare based on the parts by weight of the mineral acid per 100 parts byweight of the aqueous nitric acid. (Thus, 5% hydrochloric acid means 5parts by weight of aqueous hydrochloric acid per 100 parts by weight ofaqueous nitric acid.) For Example 9, no additional aluminum digester wasadded. The sample was worked-up and submitted for analysis. The work-upinvolved filtering the reaction mixture to isolate the HMX, washing theHMX with water to remove water and impurities from the surface of theHMX, and drying to obtain an accurate recovery weight. TABLE I wt % ofTotal HMX in Process Temp. recovered wt % NG wt % Al Example Al digesterTime (° C.) material* recovered recovered 4 5 wt % HCl at 6.0 80 980.006 0.774 3.5 hours hours after final propellant addition 5 1 wt % HClat 6.0 80 100 0.005 0.074 4 hours after hours final propellant addition6 1 wt % HCl at 6.0 80 99 0.005 0.252 4 hours after hours finalpropellant addition 7 1 wt % HCl at 4.5 84 98 0.006 0.303 1.5 hourshours after final propellant addition 8 1 wt % H₂SO₄ 6.0 80 98 0.0061.83 at 4 hours hours after final propellant addition 9 None 6.0 80 950.006 4.98 hours

Examples 10 and 11

[0045] 1000 grams of the same propellant used in Examples 4-9 were at arate of 20.4 g/min to 55 wt % nitric acid (4.1 L) at 80° C., which tookapproximately 49 minutes. The propellant was heated for 4 hours at 80°C. An of solid and acid filtrate was taken for analysis after 4 hours.HCl (277.1 grams) was added drop wise to the reaction mixture, which washeated for another 2 hours at reflux (90° C.) taking an aliquot eachhour to monitor the rate of aluminum digestion. The solid was thenfiltered and an aliquot was taken of the spent acid before the washings.The solid was washed with 4.0 L of water and then oven dried. The totalprocess time including propellant addition was 7.0 hours.

Example 12

[0046] 528 grams of the same propellant used in Examples 4-9 were addedat a rate of 20.4 g/min to 55 wt % nitric acid (2.1 L) at 80° C., whichtook 25 minutes. The propellant was heated for 2 hours at 80° C. Analiquot of solid and acid filtrate was taken for analysis after 2 hours.HCl (31.68 grams) was added drop wise to the reaction mixture, which washeated for another 2 hours at reflux (90° C.) taking an aliquot eachhour to monitor the rate of aluminum digestion. The solid was thenfiltered and an aliquot was taken of the spent acid before the washings.The solid was washed with 2.0 L of water and then oven dried. The totalprocess time including propellant addition was 4.42 hours. TABLE IIProcess wt % of time after HMX in Exam- Al propellant recovered Recoveryple digester addition material* % NG % Al (%) 10 5% HCl 6.0 100 0.007None 94 detected 11 5% HCl 6.0 100 0.006 0.003 95 12 1% HCl 4.0  990.005 1.02  95

[0047] The foregoing detailed description of the invention has beenprovided for the purpose of explaining the principles of the inventionand its practical application, thereby enabling others skilled in theart to understand the invention for various embodiments and with variousmodifications as are suited to the particular use contemplated. Thisdescription is not intended to be exhaustive or to limit the inventionto the precise embodiments disclosed. Modifications and equivalents willbe apparent to practitioners skilled in this art and are encompassedwithin the spirit and scope of the appended claims.

What is claimed is:
 1. A method of recovering a nitramine from anitramine-containing aluminized energetic material, said methodcomprising: subjecting the nitramine-containing aluminized energeticmaterial comprising aluminum, the nitramine, and at least one binder totreatment in aqueous nitric acid to digest the binder into solutionwhile neither solvating nor solvolyzing into solution at leastsubstantially all of the nitramine, adding a mineral acid, other thannitric acid, into the solution and digesting at least a portion of thealuminum; and recovering at least a portion of the nitramine, wherein aweight ratio of the aqueous nitric acid to the nitramine-containingaluminized energetic material in the treatment is in a range of about4:1 to about 6:1, and further wherein not more than 55 weight percent ofthe aqueous nitric acid consists of nitric acid.
 2. The method of claim1, wherein at least 35 weight percent of the aqueous nitric acidconsists of nitric acid.
 3. The method of claim 1, wherein saidrecovering comprises recovering at least 90 weight percent of thenitramine.
 4. The method of claim 1, wherein the treatment of thenitramine-containing aluminized energetic material comprises neithersolvating nor solvolyzing at least 98% of the nitramine of thenitramine-containing aluminized energetic material into solution.
 5. Themethod of claim 1, wherein said digesting of the aluminum comprisesdigesting at least 99 weight percent of the aluminum.
 6. The method ofclaim 1, wherein the mineral acid comprises at least one member selectedfrom the group consisting of hydrochloric acid, perchloric acid,sulfuric acid, phosphoric acid, hydrobromic acid, and hydroiodic acid.7. The method of claim 1, wherein the mineral acid compriseshydrochloric acid.
 8. The method of claim 1, wherein the mineral acid ispresent in a range of about 1 to about 50 parts by weight per 100 partsby weight of the aqueous nitric acid.
 9. The method of claim 1, whereinthe mineral acid is present in a range of about 1 to about 5 parts byweight per 100 parts by weight of the aqueous nitric acid.
 10. Themethod of claim 1, wherein the mineral acid is present in about 5 partsby weight per 100 parts by weight of the aqueous nitric acid.
 11. Themethod of claim 1, wherein the nitramine comprises at least one memberselected from the group consisting of1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane (HMX),1,3,5-trinitro-1,3,5-triaza-cyclohexane (RDX),4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo-[5.5.0.0^(5,9)0^(3,11)] -dodecane) (TEX), and2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0^(5,9)0^(3,11)]-dodecane(CL-20).
 12. A method of recovering1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane (HMX) from aluminizedenergetic material, said method comprising: subjecting the aluminizedenergetic material comprising aluminum, HMX, and at least one binder totreatment in aqueous nitric acid to digest the binder into solutionwhile neither solvating nor solvolyzing into solution at leastsubstantially all of the HMX, adding a mineral acid, other than nitricacid, into the solution and digesting at least a portion of thealuminum; and recovering at least a portion of the HMX, wherein a weightratio of the aqueous nitric acid to the aluminized energetic material inthe treatment is in a range of about 4:1 to about 6:1, and furtherwherein not more than 55 weight percent of the aqueous nitric acidconsists of nitric acid.
 13. The method of claim 12, wherein at least 35weight percent of the aqueous nitric acid consists of nitric acid. 14.The method of claim 12, wherein said recovering comprises recovering atleast 90 weight percent of the HMX.
 15. The method of claim 12, whereinthe treatment of the aluminized energetic material comprises neithersolvating nor solvolyzing at least 98% of the HMX of the energeticmaterial into solution.
 16. The method of claim 12, wherein saiddigesting of the aluminum comprises digesting at least 99 weight percentof the aluminum.
 17. The method of claim 12, wherein the mineral acidcomprises at least one member selected from the group consisting ofhydrochloric acid, perchloric acid, sulfuric acid, phosphoric acid,hydrobromic acid, and hydroiodic acid.
 18. The method of claim 12,wherein the mineral acid comprises hydrochloric acid.
 19. The method ofclaim 12, wherein the mineral acid is present in a range of about 1 toabout 50 parts by weight per 100 parts by weight of the aqueous nitricacid.
 20. The method of claim 12, wherein the mineral acid is present ina range of about 1 to about 5 parts by weight per 100 parts by weight ofthe aqueous nitric acid.
 21. The method of claim 12, wherein the mineralacid is present in about 5 parts by weight per 100 parts by weight ofthe aqueous nitric acid.